1. Field of the Invention
The invention relates to a coupling mechanism for a refrigerant compressor, and more particularly, to a mechanism for disconnecting the drive shaft of the compressor from a drive pulley in the event of a compressor failure or malfunction.
2. Description of the Prior Art
In a standard automotive air conditioning system, an electromagnetic clutch is interposed between the automotive engine and the drive shaft of the compressor to intermittently transmit the rotational driving force of the engine to the drive shaft. The operation of the electromagnetic clutch is controlled by a change in the operating conditions of the air conditioning system, e.g., a change of temperature in the passenger compartment.
In the event of a compressor failure or malfunction, the clutch should operate to disconnect the engine from the compressor to prevent transmission of the rotational driving force from the engine. Nevertheless, because the clutch is usually loaded in a compressor which has a variable displacement mechanism enabling the compressor to change its capacity in direct response to changes in operating conditions, the electromagnetic clutch is not necessary to obtain satisfactory control of the refrigeration or temperature condition of the air conditioning system. It is necessary, however, to provide the compressor with a safety mechanism to prevent damage to other parts of the engine or the air conditioning system in the event of a compressor failure or malfunction. The electromagnetic clutch serves as an expensive solution to this problem.
One example of an automotive air conditioning system compressor which does not made use of an electromagnetic clutch is disclosed in U.S. Pat. No. 3,861,829 to Roberts et al. Moreover, the present invention constitutes a novel and advantageous improvement over the coupling mechanism for compressors disclosed in U.S. Pat. No. 4,859,156 to Kirkuchi, which is incorporated herein by reference. As shown in the compressor of FIG. 1, the compressor includes compressor housing 10 and front end plate 11 attached to an open end of housing 10. Drive shaft 12 is rotatably supported within front end plate 11. Tubular extension 1 la extends outwardly from front end plate 11 and surrounds drive shaft 12.
Pulley 14 is rotatably supported on the peripheral outer surface of tubular extension 11a through bearing 15. Pulley 14 is securely fitted on the peripheral outer surface of bearing 15 by snap ring 26 disposed between the inner surface of pulley 14 and the inner end surface, with respect to housing 10, of bearing 15. Moreover, snap ring 26 prevents pulley 14 from moving parallel to the rotational axis of drive shaft 12. Bearing 15 is secured between flange 11b and snap ring 19 which is fixed on the peripheral outer surface of tubular extension 11a.
Armature 13 has a centrally located hole and is secured on the terminal outer end portion of drive shaft 12 by a bolt 12a and a nut 33. Armature 13 is also coupled with drive shaft 12 by the interaction of key 20 on the end of drive shaft 12 with key groove 22 in the centrally located hole of plate-like element 13.
A plurality of cylindrical members 28 are disposed between the inner axial surface, with respect to housing 10, of armature 13 and the outer axial surface, also with respect to housing 10, of pulley 14 to couple armature 13 to pulley 14. Holes 13a are formed on the inner axial surface of armature 13, and one end of each cylindrical member 28 is disposed therein. The other end of each cylindrical member 28 is disposed in corresponding hole 14a formed on the outer axial surface of pulley 14. Cylindrical members 28 may be made of synthetic resins or metals which are easily broken if a large torque acts between pulley 14 and armature 13, i.e., a sufficiently large force which acts to rotate pulley 14 with respect to armature 13.
In ordinary operation of such a coupling mechanism, the driving force of the engine is transmitted to pulley 14 by a belt (not shown) and is then transferred to drive shaft 12 of a compressor through cylindrical members 28 and armature 13. In this manner, drive shaft 12 is rotated. If, during the operation of the compressor, a failure or malfunction occurs, and as a result of the failure or malfunction the rotation of drive shaft 12 is interrupted, the rotation of armature 13 is also interrupted due to the coupling of armature 13 with drive shaft 12. Nevertheless, a large rotational force is still provided to pulley 14 by the engine, and pulley 14 consequently provides a large torque to armature 13 through cylindrical members 28. This torque is sufficient to break cylindrical members 28 because cylindrical members 28 are designed to break when such a torque is applied. As a result, pulley 14 is disconnected from armature 13 and is free to rotate without resistance applied through armature 13 from motionless drive shaft 12. The maximum acceptable amount of torque and consequently, the size, material, and number of cylindrical members 28 is dependent on the air conditioning system and the compressor with which the coupling mechanism is used.
This configuration, however, has certain disadvantages. If the compressor should lock or become difficult to rotate due to compressor failure or malfunction, pulley 14 is subjected to excessive torque through cylindrical members 28. When this torque breaks cylindrical members 28, each cylindrical member 28 may be broken at a different location, i.e., one cylindrical member 28 may be broken on armature 13 side while another is broken on pulley 14 side. As a result, the broken sections of cylindrical members 28 contact or bite each other, and pulley 14 cannot be sufficiently disconnected from armature 13 to allow it to rotate freely. Therefore, the torque applied through these contacts or bites is likely to damage the engine and other parts of the driving system, such as the alternator, a cooling fan, or a power steering mechanism, which rotate together by the belt.
Further, in this configuration, the diameters of holes 13a of armature 13 and holes 14a of pulley 14 should be almost the same as the diameter of cylindrical member 28 because both ends of each cylindrical member 28 must be inserted tightly into holes 13a and holes 14a to securely connect armature 6 with pulley 14. Therefore, if these diameters are different from each other due to an error in manufacturing, it usually prevents the armature 13 from being secured to pulley 14 during assembly.